One final question on this one. As per latest comments this works great, but is there a way so the presentation pages in the appendix are made-up landscape as they are now, but are rotated 90 degrees so they are created in the pdf document as the first two pages.

\startbuffer[slides]
\setuptolerance[
  horizontal,
  tolerant,
  stretch]

\setuppapersize[
  A4,landscape]

\setuplayout[
  width=middle,
  backspace=35mm,
  cutspace=35mm,
  height=middle,
  topspace=5mm,
  bottomspace=20mm]

\setuppagenumbering[
  location={footer,center}]

\setuphead
  [section]
  [page={yes}]

\usetypescript[pagella]
\setupbodyfont[pagella,18pt]
\setupbodyfontenvironment[
  28pt][  % For body
  d=36pt, % For title
  a=12pt, % For author & date
  ]
\setuptype[style=medium]
\setuptyping[typing][bodyfont=16pt]

\setupwhitespace[medium]

\setbreakpoints[compound]

\setuphead[chapter][style=\bfd]
\setuphead[section][style=\bfc]
\setuphead[subsection][style=\bfb]
\setuphead[subsubsection][style=\bf]

\setupitemize[autointro] % prevent orphan list intro
\setupitemize[indentnext=no]

\starttext

\startsection[title={MySlideTitle},ref={myref1}]

Body text

\startitemize
\item Item 1
\item Item 2
\stopitemize

\stopsection

\startsection[title={MySlideTitle},ref={myref2}]

Body text

\startitemize
\item Item 1
\item Item 2
\stopitemize

\stopsection

\stoptext\starttext
text

\stoptext
\stopbuffer

  \savebuffer[list=slides, file=slides.tex]

  \starttext
  \startbodymatter
  \dorecurse{10}{\input zapf\par}
  \typesetfile[\jobname-slides.tex][--purgeall][object=no, width=0pt]
  \stopbodymatter
  \startappendices
  \getfiguredimensions[\jobname-slides.pdf]
  \dorecurse{\noffigurepages}
      {\startTEXpage
        \externalfigure[\jobname-slides.pdf][page=\recurselevel]
       \stopTEXpage}
  \stopappendices